挤压铸造短纤维增强金属基复合材料浸渗过程分析

在分析挤压铸造金属基复合材料浸渗条件的基础上，建立了液态金属在短纤维预制件中的浸渗和压力分布模型，计算结果表明：（１）当外加压力不足以使短纤维预制件产生变形之前，其浸渗距离和浸渍前端的压力分别为：Ｘｆ＝１－Ｆ／１－Ｖ＇ｆ∫＾ｔ０ｕｄｔ和Ｐｓ＝μｕ／Ｋ＇０·１－Ｆ／１－Ｖ＇ｆ∫＾ｔ０ｕｄｔ－４Ｖｆ０γｃｏｓθ／ｄｆ（１－Ｖｆ１０）（２）当外加压力使短纤维预制件产生变形之后，其浸渗距离和浸渗前端的压力     

腐蚀磨损数学模型

测试了化学镀Ｎｉ－Ｐ合金静腐蚀、动腐蚀和腐蚀磨损试验结果。通过对试验结果的处理，建立了动腐蚀速率和腐蚀磨损速率与冲击速度Ｖ、介质浓度Ｃ的数学模型：Ｖ＝Ｋ１Ｖ＾ｎ１＋Ｋ２Ｖ＾ｎ２Ｃ＾ａ（ａ＝Ｋ３Ｖ＾ｎ３）。建立了腐蚀磨损速率Ｖｗｃ与纯磨损速率Ｖｗｏ、纯腐蚀速率Ｖｐｃ及动腐蚀速率Ｖｏｃ之间数学模型：Ｖｗｃ＝Ｖｗｏ＋Ｖｐｃ＋ＫｗｃＶｗｏ，Ｖｐｃ＝Ｖｗｏ＋（１＋Ｋｗ）Ｖｏｃ＋Ｋｗｃ（１＋Ｋｗ）ＶｗｃＶｏｃ     

螺纹三个中径的关系：兼与余晓芬同志商榷

本文认为当Δ（α／２）＝０时，ｄ作＝ｄ单＋ｆｐ是不成立的。ｄ作＝ｄ中＋ｆｐ才是正确的计算公式     

单向短纤维增强复合材料的复模量

本文提出了单向短纤维增强复合材材纤维方向模量的一个计算模型.这个模型考虑了横向相邻纤维间以及纵向相接纤维间的相互作用.籍助于这一模型,根据粘弹性对应原理,本文用解析方法计算了单向短纤维增强复合材料的纤维方向复模量,着重分析了端部间隙对复模量的实部和虚部的影响.计算结果和文献中已有的计算结果和试验结果作了比较.      

多元线性超结构关系模型参数估计的大样本性质

讨论了如下线性超结构关系模型βｘｋ＋α＝０，ζｋ＝ｘｋ＋εｋｋ＝１，２，．．．ｎ，（εｋ，ｋ＝１，２，．．．ｎ）ｉ，ｉ，ｄ，Ｅ（ε１）＝０，Ｖａｒ（ε１）＝σ＾Ｉｍ其中（ｘｋ，ｋ＝１，２，．．．．，ｎ）为相互独立的ｍ维ｒ．ｖ．列，且和随机误差（ε，ｋ＝１，２，．．．．，ｎ）相互独立，在一定条件下，证明了ＬＳ估计量β，α，σ＾２的强相合性，唯一性，并给出了估计量的一类ａ．ｓ．收敛速度０（ｎ＾－１／２     

环十二酮肟在硫酸中热效应

使用ＲＤ－１型热导式自动量热计测量了不同温度下环十二酮肟在９８％硫酸中热效应。结果表明：当Ｔ＜３３３Ｋ时，仅产生溶解热效应，３０３Ｋ下溶解热△Ｈ＿（ｓ，ｍ）＝－５１．７ｋＪ·ｍｏｌ￣（－１）（ｍ＝４．２８５ｍｏｌ·ｋｇ￣（－１））；当Ｔ＞３４３Ｋ时发生环十二酮肟重排反应，３９３Ｋ下反应热△Ｈ＿（Ｒ，ｍ）＝－２３１．８ｋＪ·ｍｏｌ￣（－１）（ｍ＝４．９６×１０￣（－３）ｍｏｌ·ｋｇ￣（－１））和△Ｈ＿（Ｒ，ｍ）＝－２３７．０ｋＪ·ｍｏｌ￣（－１）（ｍ＝１．７×１０￣（－２）ｍｏｌ·ｋｇ￣（－１））。     

第八讲：真空系统设计

④考虑管口影响时，圆管的流导（上接１９９８年第５期第４７页）设圆管的长度为Ｌ，半径为Ｒ，直径为Ｄ＝２Ｒ。在分子流条件下，考虑管口影响时，圆管的流导几率ｐｒ如下：当Ｌ／Ｒ≤１．５时，ｐｒ＝１１＋Ｌ２Ｒ当Ｌ／Ｒ＞１．５时，ｐｒ＝２０＋８ＬＲ２０＋１９ＬＲ...     

双参数指数分布下两应力交叉步加试验的统计分析

设产品寿命服从双参数指数分布，失效率和保证寿命的加速模型分别为ｌｎθｉｊ＝β０＋β１ψ１（Ｓｉｊ）＋β２ψ２（Ｓ２ｊ）＋β３ψ１（Ｓ１ｉ（ψ２（Ｓ２ｉ） ｕｉｊ＝α０－α１ｆ１（Ｓ１ｉｊ）－α２ｆ２（Ｓ２ｊ） ｉ＝１，２，…，ｌ，ｊ＝１，２，３…，ｋ，本文研究了用两应力交叉步加试验的数据对参数βｉ和αｊ进行估计和检验，然后由模型要以求得正常工作应力下各种可靠性牲特征的估计值。     

φ形式的Khintchine不等式

推广Ｋｈｉｎｔｃｈｉｎｅ不等式，对于一类φ函数，得到φ－１Σｎ１φ（｜ａｊ｜）≤ｃ１２ｎΣε１…Σεｎ｜ε１ａ１＋…＋εｎａｎ｜其中εｉ＝±１，Σ对所有（ε１，…，εｎ）取值作为应用，得到Ｈ１函数的小波级数的一个φ不等式：∫Ｒｎφ－１Σλ∈Ｆφ（｜（ｆ，ψλ）ψλ（ｘ）｜）ｄｘ≤ｃ     

组成对Bi系微晶玻璃超导纤维性能的影响

用熔体快速淬冷法制备了数种Ｂｉ（Ｐｂ）ＳｒＣａＣｕＯ玻璃，进而用动态加热荷重法将这些玻璃拉成纤维。用Ｘ射线衍射、差热分析、电子探针和能谱及电流测量、拉丝试验等手段研究了玻璃成分变化对成丝能力和晶化后超导性能的影响。结果表明，Ｓｒ、Ｃａ含量的变化不仅对超导性能，而且对玻璃成丝能力有很大影响。获得的超导纤维的最大长度为５３ｃｍ，在７７Ｋ和零磁场下超导短纤维的最高电流密度Ｊｃ＝１５Ａ／ｃｍ＾２。     

注塑成型纤维增强热塑性树脂复合材料刚度预测方法

基于Hsueh模型的应力场分布,采用代表性体积单元(RVE)平均近似方法,推导出可以退化成Halpin-Tsai模型的泊松比ν₁₂的显性表达式,与桥联模型基本重合。结合Fu模型和Giner模型,引入与纤维长径比(l/a)相关的指数衰减函数得到横向模量E₂₂修正的Halpin-Tsai模型,与自洽模型重合。基于泊松比各向同性假设而推导出的泊松比ν₂₃与有限元结果逼近,远优于Halpin-Tsai模型;基于逆向工程,修正了被Halpin-Tsai模型低估的剪切模量G₂₃。基于经典的层合板分析方法(LAA),引入纤维长度分布(FLD)及纤维取向广义分布函数,对两种注塑成型短玻璃纤维增强热塑性树脂(FRT)复合材料的弹性常数进行预测。结果表明:4个微观力学组合模型均很好地预测了复合材料的弹性常数,但纤维长度质量分布的预测结果比纤维长度数量分布的结果更为合理,特别是对于纵向杨氏模量E_L的改进效果大于5%。      

洋麻纤维增强全降解复合材料的制备及其弯曲模量

利用压制成型工艺制备了洋麻纤维增强全降解复合材料, 分析了纤维体积分数、长度以及取向分布对材料弯曲模量的影响, 并根据COX 剪滞法和洋麻纤维在成型后被压缩的结构特点, 探讨了一种修正COX 剪滞模型对弯曲模量的预测。实验表明, 随着纤维体积分数、长度和取向因子的增加, 材料的弯曲模量增加。扫描电镜的观察显示洋麻纤维的横断面呈现多孔状结构, 成型后受到压缩而变得致密, 增加了材料的弯曲模量。预测结果表明, 结合了纤维压缩率的修正模型的预测计算值与实验值取得较好的一致。      

Tensile Elastic Modulus, Strength and Fracture of δ-Al_2O_(3f)/Al Alloy Composites

1. IntroductionThe tensile elastic modulus and strength are twoimportal material parameters of composites and hadbeen paid more attention by mad researchers[1-4].However, in the random short fiber reinforced metalmatrix composite (RSFRMMC), the tensile elasticmodulus and strength are influenced by many factorsand have not been predicted precisely. At present,the predicting precision for elastic modulus of corn-posites had been improved by using the finite elementmethod (FEM)l']. However, t…     

有一定取向性的碳纤维增强尼龙6复合材料弹性模量的实验和理论研究

纤维增强热塑性聚合物基复合材料注塑成型后往往被认为是各向同性复合材料。然而,注塑成型后纤维会具有一定的取向性,从而使复合材料试样呈现各向异性的特点。为了合理预测此类复合材料的弹性模量,本文对碳纤维增强尼龙6复合材料注塑试样内部的纤维长度和取向分布情况进行了测试和分析,得出了纤维取向的分布规律。随后结合单向纤维增强聚合物基复合材料力学模型和层叠理论,构造出了适用于有一定取向性的纤维增强树脂基复合材料弹性模量预测理论模型,其理论结果和拉伸实验结果吻合较好,表明该预测模型的准确性比较高。      

Continuous carbon nanotube reinforced composites

Carbon nanotubes are considered short fibers, and polymer composites with nanotube fillers are always analogues of random, short fiber composites. The real structural carbon fiber composites, on the other hand, always contain carbon fiber reinforcements where fibers run continuously through the composite matrix. With the recent optimization in aligned nanotube growth, samples of nanotubes in macroscopic lengths have become available, and this allows the creation of composites that are similar to the continuous fiber composites with individual nanotubes running continuously through the composite body. This allows the proper utilization of the extreme high modulus and strength predicted for nanotubes in structural composites. Here, we fabricate such continuous nanotube polymer composites with continuous nanotube reinforcements and report that under compressive loadings, the nanotube composites can generate more than an order of magnitude improvement in the longitudinal modulus (up to 3,300%) as well as damping capability (up to 2,100%). It is also observed that composites with a random distribution of nanotubes of same length and similar filler fraction provide three times less effective reinforcement in composites.     

Coefficients of nonlinear thermal expansion for fiber-reinforced composites

In the present study, a micromechanics model is proposed to predict the coefficients of nonlinear thermal expansion (CTEs) of fiber-reinforced composites. The influence of fiber aspect ratio on the CTEs is also investigated. It is noted that the parameters of fiber aspect ratio have a significant effect on both the longitudinal CTEs and transverse CTEs. The CTEs of composites are also very sensitive to the different fiber volume fractions. Moreover, the Young’s modulus and Poisson’s ratio of composites are taken into account in the present analysis. The theoretical derivations are applicable for the composites under mechanical or thermal environment conditions. The present model offers a direct prediction of CTEs and can account for the effects of fiber aspect ratio and volume fractions.     

复合材料横向压缩性能的研究

本文考察了由两种力学性能不同的基体制备的玻璃纤维、碳纤维和碳/玻混杂纤维复合材料的横向压缩性能及破坏特征,导出了估算复合材料横向压缩强度半经验公式,其估算值与实测值比较吻合。      

Effects of mean stress and stress concentration on fatigue behavior of short fiber reinforced polymer composites

An experimental study was conducted to evaluate the effect of mean stress on fatigue behavior of two short glass fiber reinforced thermoplastic composites and the effect of stress concentration on fatigue behavior of an unreinforced and a short glass fiber reinforced thermoplastic. Load‐controlled fatigue tests were conducted on unnotched (smooth) specimens at R ratios of ?1, 0.1, and 0.3 in different mold flow directions or fiber orientations and at a range of temperatures between ?40 and 125 °C. Effect of mean stress on fatigue life was found to be significant at all temperatures. Several mean stress parameters including modified Goodman, Walker, and Smith–Watson–Topper were evaluated for their ability to correlate mean stress data. A general fatigue life prediction model was also used to account for the effect of mean stress, temperature, and fiber orientation. Notched fatigue tests of an unreinforced polymer and a short glass fiber thermoplastic composite were also conducted using plate type specimens with a central circular hole and with or without the presence of mean stress. Effect of stress concentration was found to be considerable, with or without mean stress and in both the longitudinal and transverse directions. The commonly used Neuber's rule for metallic materials, nonlinear finite element analysis, as well as critical distance approaches were utilized for notch deformation and fatigue life analyses.     

混杂纤维复合材料的拉伸刚度

对单向和多向混杂纤维复合材料的拉伸刚度进行了研究。在混合定律的基础上考虑混杂比和分散度对混杂效应的影响, 提出了单向混杂纤维复合材料拉伸模量的估算公式。通过实验得到了多向混杂纤维复合材料的拉伸模量, 并且采用经典层合板理论进行了估算, 基于混杂比以及分散度对拉伸模量的影响规律, 对多向混杂纤维复合材料拉伸模量的估算公式进行了修正。结果表明: 混杂纤维复合材料的拉伸模量与混杂比和分散度相关, 分散度的增大在一定程度上可以提高单向混杂纤维复合材料的纵向拉伸模量。采用经典层合板理论所得的拉伸模量与实验值有一定的误差, 而本文所提出的公式能够更加准确地估算混杂纤维复合材料的拉伸模量。      

界面对硅酸铝短纤维增强AZ91D镁基复合材料蠕变性能的影响

界面对复合材料蠕变性能的影响很大。在试验分析的基础上建立了硅酸铝短纤维增强AZ91D镁基复合材料理论分析模型,利用三维有限元分析方法,系统研究了界面特性、界面上应力应变分布和短纤维位向变化对硅酸铝短纤维增强AZ91D镁基复合材料蠕变性能的影响。研究表明：界面特性,如厚度、模量,均对纤维最大轴应力和稳态蠕变速率有影响,当界面厚度增加,纤维最大轴应力减小而稳态蠕变速率增大;当界面模量增大,纤维最大轴应力增大而稳态蠕变速率减小,但当界面模量高于基体模量时,纤维最大轴应力和稳态蠕变速率均保持不变;纤维位向也影响轴应力分布和稳态蠕变速率,纤维在其末端界面上存在较大的应力和应变,此处容易产生微裂纹而使材料抗蠕变能力下降;界面对硅酸铝短纤维增强AZ91D镁基复合材料的蠕变曲线和蠕变断裂机制也有影响,其影响程度还与纤维位向有关。